GRAND PRAIRIE -- A Grand Prairie middle school teacher abruptly resigned and walked into a Grand Prairie police station to turn herself in to police Tuesday morning, telling officers that she is the driver they were searching for in the hit-and-run death of a 6-year-old boy last week.

Tammy Lowe, 53, is being held in the Grand Prairie detention center in lieu of $200,000 bail on charges of manslaughter, a second-degree felony, and failure to stop and render aid, a third-degree felony, police said. Lowe was a seventh-grade social studies teacher at Adams Middle School.

John Raidy, a student at Austin Elementary School, was crossing North Carrier Parkway at Holiday Hills Drive at about 7:30 p.m. Thursday when he was hit by a southbound vehicle that ran the red light, police said. Police have been searching since then for the driver of that vehicle, who they said "stopped briefly" but then fled the scene.

John was taken by ambulance to Arlington Memorial Hospital where he died, police said.

Just hours before police were set to release new information to local media Tuesday about the vehicle involved, Lowe reportedly walked into the police station with her husband and said she was the driver at fault. Police said Lowe was distraught and appeared "like she hadn't slept in days."

"This is a horrific event and she did the right thing by turning herself in," Detective Lyle Gensler said.

Police seized Lowe's vehicle, a 2008 Toyota Yaris, from her Grand Prairie home. That vehicle had a dent in its hood "consistent with hitting a small pedestrian," Sgt. Eric Hansen said. It is also the same make and model that has been identified in surveillance footage of the fatal incident, police said.

Raidy was just a few feet ahead of his mother, who was pushing a 2-year-old child in stroller, when he began crossing the intersection.

The family had the green light, and the car's signal had been red for 14 seconds when the driver ran it, according to police.

Details about what Lowe was doing at the time of the crash have not yet been made public. She was reportedly alone in the vehicle and "there was no braking until the collision," police said.

"She knew that it had happened and left the scene," Gensler said.

Before she turned herself in, Lowe left a hand-written letter of resignation on her principal's desk at Adams Middle School Tuesday morning and then left the campus, district spokesman Sam Buchmeyer said. The letter did not indicate her involvement in the traffic fatality, he said.

Lowe's abrupt resignation, coupled with colleagues' reports about her recent unusual behavior, prompted the district to send a school resource officer to her home Tuesday to conduct a welfare check, Buchmeyer said.

"They said her behavior was not quite as it had been before. They could tell something was amiss," Buchmeyer said.

Lowe had been employed as a teacher with the district since the 1996-1997 school year. Counselors will be at Adams Middle School to assist Lowe's colleagues and students.

Anita Eads, John's grandmother, told WFAA/Channel 8 that the family is gaining some comfort now that a suspect has been arrested and that they will be able to bury the boy with "a little lighter heart."

Eads told the television station that she felt some sympathy for Lowe.

"I know that woman didn't set out to hit him," Eads said. "I can only imagine what she's going through right now."